The present invention relates to a power unit of a motorcycle such as a scooter-type vehicle or the like.
Generally, the power unit of the scooter-type vehicle has a structure in which a belt-type transmission unit (speed change mechanism or change gear) is integrally connected to a rear portion of an engine and a rear wheel is directly pivoted to a most rear section of the transmission unit. A front portion of the power unit is pivoted to a body frame of a motorcycle (which may be called vehicle body frame, hereinlater) and a rear portion thereof is suspended to the vehicle body frame by means of a shock absorber, so that a whole of the power unit is swung entirely vertically together with the rear wheel so as to achieve a part of a swing arm of the rear wheel.
In accordance with the structure mentioned above, it becomes advantageous that a capacity of a luggage space placed above the power unit can be secured to be increased and a riding function (running felling) can be improved by making an engine vibration hard to be transmitted to the frame side. However, on the contrary, since a weight of the whole of the power unit becomes heavy in the case that a displacement of the engine is increased, a shared weight of the rear wheel is increased, a weight may be improperly distributed between front and rear wheels and a support rigidity of the rear wheel becomes insufficient. In such case, arrangement or layout of respective parts or elements of a motorcycle may be restricted.
Then, as shown in Japanese Patent Laid-Open Publications Nos. HEI 10-324287 (Prior Art 1) and HEI 11-129969 (Prior Art 2), there have been developed a scooter-type vehicle in which an engine and a transmission unit are fixed to a vehicle body frame side and only a shaft drive apparatus extending rearward from the transmission unit is made vertically swingable so as to drive the rear wheel. Accordingly, it is possible to mount an engine corresponding to a heavy load, which is the same as that in the normal motorcycle to a front side of the vehicle body frame so as to make a weight distribution between the front and rear wheels proper.
However, in the structure described in the above Prior Art 1, since a drive pulley, a driven pulley, a belt and the like in the transmission unit are exposed, the transmission is easily damaged by foreign materials such as dirt, sands, stones or the like splashed by the rear wheel during a running of a motorcycle.
On the contrary, in the structure described in the above Prior Art 2, since a drive pulley of the transmission unit is coaxially provided in a crankshaft of an engine, a whole of the transmission unit protrudes sideward. Accordingly, this apparatus lacks a compact size.
Further, since the engine, the transmission and a bevel gear mechanism corresponding to an output take-out portion are received within one casing so as to be united, it is necessary to produce and assemble all of the parts mentioned above at the same production site, so that a productivity is significantly made worse. Further, in the case of intending to change any one of specifications such as an engine output, a gear ratio or the like, it is necessary to change a whole of the unit, so that it is hard to apply the unit to various kinds of vehicles. Additionally, in the case of performing maintenance of any one portion, it is necessary to disassemble a whole of the unit, which may deteriorate the ease maintenance.
An object of the present invention is to substantially eliminate disadvantages or inconveniences encountered in the prior arts mentioned above and to provide a power unit of a motorcycle capable of making a power unit compact, improving a productivity thereof, making ease of maintenance, improving a manufacturing quality and the like, and moreover, the present invention makes it possible to be applied to various kinds of vehicles to reduce processing man-hours. It also becomes possible to well secure a rigidity of the power unit itself and a support rigidity of the power unit to the vehicle body frame.
This and other objects can be achieved according to the present invention by providing a power unit of a motorcycle comprising:
an engine unit in which a counter shaft rotating while interlocking with a crankshaft is supported in parallel at a rear portion in a casing of an engine body provided with the crankshaft disposed along a width direction of a motorcycle body, and a bracket portion having a fitting hole extending rearward so as to pass through in the width direction of the motorcycle body is formed in a rear portion outside the casing;
a transmission unit in which an input shaft and an output shaft are pivoted at front and rear portions in another casing different from the casing of the engine unit so as to constitute a transmission device; and
a bevel unit receiving a bevel input shaft disposed along the width direction of the motorcycle body, a bevel output shaft disposed along a longitudinal direction of the motorcycle body and a bevel gear which are all disposed in a further casing so as to take out an engine output rearward from the bevel output shaft,
wherein one side surface of a front portion, in the longitudinal direction of the motorcycle body, of the transmission unit is fixed to one side surface of a rear portion of the casing in the engine unit so as to connect the counter shaft to the input shaft to be integrally rotatable, a bearing boss of the output shaft is closely fitted to the fitting hole in the bracket portion with one side surface of the rear portion of the transmission unit being disposed adjacent to one side surface of the bracket portion of the engine unit, and the bearing boss of the bevel input shaft is closely fitted and fixed to the fitting hole of the bracket portion with the bevel unit being disposed adjacent to another side surface of the bracket portion so as to connect the output shaft to the bevel input shaft to be integrally rotatable.
In a preferred embodiment of the above aspect, the counter shaft receiving portion of the engine unit is arranged, in an offset manner, close to one side with respect to a center line of the motorcycle body in a plan view and the bracket portion is extended to a rear portion thereof so as to provide a plan shape of the engine unit to be a substantially L shape and a plan shape of the transmission unit is formed in a substantially L shape to thereby arrange the transmission unit on a side of the center line of the motorcycle body in the bracket portion so as to assemble substantially L-shaped portions of the engine unit and the transmission unit with each other to provide a substantially rectangular shape, and on the other hand, the bevel unit is arranged on a side opposite to the center line of the vehicle body in the bracket portion.
The bracket portion of the engine unit, the transmission unit and the bevel unit are fastened together by a fastening member disposed along the width direction of the motorcycle body.
The motorcycle body frame fixing portion of the power unit is formed to the bracket portion of the engine unit.
The transmission device is a belt-type change gear device disposed in the another casing having a three-piece structure. The belt-type change gear device includes an input shaft supported in parallel to the crankshaft of the engine unit and the input shaft is operatively coupled with the bevel input shaft.
According to the structures and characters of the power unit of the motorcycle such as scooter-type vehicle of the present invention mentioned above, since the engine unit, the transmission unit and the bevel unit can be respectively manufactured in different production sites, a productivity and ease of maintenance of the power unit are improved and it is possible to apply to various kinds of vehicles. Furthermore, since the structure is made such that the transmission unit and the bevel unit are coaxially fitted and fixed to the fitting hole of the bracket portion in the engine unit, a manufacturing quality can be improved and processing man-hours can be reduced, and further a rigidity of a whole of the power unit is increased.
Furthermore, in accordance with the structure mentioned above, since no dead space is generated between the engine unit and the transmission unit, and there is no case that any one of the transmission unit and the bevel unit arranged laterally at the back of the engine unit protrudes widely to a side direction from a lateral width of the engine unit, sizes in a longitudinal direction and a width direction of the power unit can be made compact.
In comparison with the case that the transmission unit and the bevel unit are respectively fastened by exclusive fastening members, since the number of the fastening members is reduced, and assembling man-hours can be reduced accordingly, a productivity of the power unit can be improved.
Still furthermore, since the connecting portions of the respective units constituting the power unit are fixed to the vehicle body frame, the supporting rigidity of the whole of the power unit can be increased.
As mentioned above, in summary, in accordance with the power unit of the motorcycle of the present invention, it is possible to make a power unit compact, to improve a productivity, ease of maintenance, a manufacturing quality and the like, to make it possible to be applied to various kinds of vehicles, to reduce processing man-hours, and to secure a rigidity of the power unit itself and a support rigidity of the power unit to the vehicle body frame.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.